It has long been a common practice to start internal combustion engines using the energy stored in batteries to drive starter motors, which in turn crank the engine until the engine starts. However, the load placed upon the batteries reduces the life of service of the batteries significantly. A typical battery for starting an engine may only have a useful life of about three years. In addition, the power output of even a good battery may be severely reduced when used under extreme temperature conditions.
Advances have been made in technology regarding capacitors, which are capable of storing electrical energy, but until recently were not capable of storing the amounts of energy needed to start an engine. However, large capacitance capacitors, for example electric double layer capacitors, have been developed which are capable of storing large amounts of electric charge. These capacitors are sometimes known as super capacitors, and are finding use in applications such as in engine starting circuits.
For example, in U.S. Pat. No. 5,157,267, Shirata et al. (Shirata) disclose an apparatus for starting an engine which uses a capacitor in parallel with a starting battery. The battery charges the capacitor through a boost controller, i.e., a DC to DC inverter, to a voltage slightly higher than the battery voltage. For example, for a battery voltage of 12 volts, the capacitor would be charged to 14 volts. The energy stored in the capacitor is then used to start the engine, as the battery continues to charge the capacitor during the start cycle.
Although the apparatus of Shirata uses a capacitor to start an engine, the battery must still continue to work under load to maintain a charge on the capacitor. Therefore, the battery must still be subjected to the stresses of continual quick-draining charge-discharge cycles, thus shortening the useful life of the battery. It would be desirable to provide a starting system for an engine which did not subject the battery to constant discharging and charging during the starting process.
In addition, it may be desired to provide a voltage for starting an engine that is much higher than a battery is capable of providing. For example, a large engine may employ multiple starters in the starting system. These starters are typically connected in parallel to accept a constant voltage, e.g., 36 volts, from a battery source. However, the current requirements for multiple starters in parallel is tremendous, e.g., 3,000 amps. It may be desired to connect the starters in series to maintain a relatively low current drain, e.g., 1,000 amps. Components, as well as the wiring, in the starting system could be used at lower ratings and dimensions. The starters connected in series, however, would require a higher voltage, e.g., about 100 volts. A capacitor charged over a long period of time by a low voltage battery, e.g., one or more batteries providing 36 volts, through an inverter, could store a charge in a capacitor at 100 volts to be used to drive the starters as needed.
The present invention is directed to overcome one or more of the problems set forth above.